Nucleic acid therapeutics have promise for treating diseases ranging from inherited disorders to acquired conditions such as cancer, infectious disorders (AIDS), heart disease, arthritis, and neurodegenerative disorders (e.g., Parkinson's and Alzheimer's). Not only can functional genes be delivered to repair a genetic deficiency or induce expression of exogenous gene products, but nucleic acid can also be delivered to inhibit endogenous gene expression to provide a therapeutic effect. Inhibition of gene expression can be mediated by, e.g., antisense oligonucleotides, double-stranded RNAs (e.g., siRNAs, miRNAs), or ribozymes.
A key step for such therapy is to deliver nucleic acid molecules into cells in vivo. However, in vivo delivery of nucleic acid molecules, in particular RNA molecules, faces a number of technical hurdles. First, due to cellular and serum nucleases, the half life of RNA injected in vivo is only about 70 seconds (see, e.g., Kurreck, Eur. J. Bioch. 270:1628-44 (2003)). Efforts have been made to increase stability of injected RNA by the use of chemical modifications; however, there are several instances where chemical alterations led to increased cytotoxic effects or loss of or decreased function. In one specific example, cells were intolerant to doses of an RNAi duplex in which every second phosphate was replaced by phosphorothioate (Harborth, et al, Antisense Nucleic Acid Drug Rev. 13(2): 83-105 (2003)). As such, there is a need to develop delivery systems that can deliver sufficient amounts of nucleic acid molecules (in particular RNA molecules) in vivo to elicit a therapeutic response, but that are not toxic to the host.
Nucleic acid based vaccines are an attractive approach to vaccination. For example, intramuscular (IM) immunization of plasmid DNA encoding for antigen can induce cellular and humoral immune responses and protect against challenge. DNA vaccines offer certain advantages over traditional vaccines using protein antigens, or attenuated pathogens. For example, as compared to protein vaccines, DNA vaccines can be more effective in producing a properly folded antigen in its native conformation, and in generating a cellular immune response. DNA vaccines also do not have some of the safety problems associated with killed or attenuated pathogens. For example, a killed viral preparation may contain residual live viruses, and an attenuated virus may mutate and revert to a pathogenic phenotype.
Another limitation of nucleic acid based vaccines is that large doses of nucleic acid are generally required to obtain potent immune responses in non-human primates and humans. Therefore, delivery systems and adjuvants are required to enhance the potency of nucleic acid based vaccines. Various methods have been developed for introducing nucleic acid molecules into cells, such as calcium phosphate transfection, polyprene transfection, protoplast fusion, electroporation, microinjection and lipofection.
Cationic lipids have been widely formulated as liposomes to deliver genes into cells. However, even a small amount of serum (˜10%) can dramatically reduce the transfection activity of liposome/DNA complexes because serum contains anionic materials. Recently, cationic lipid emulsion was developed to deliver DNA molecules into cells. See, e.g., Kim, et al., International Journal of Pharmaceutics, 295, 35-45 (2005).
U.S. Pat. Nos. 6,753,015 and 6,855,492 describe a method of delivering nucleic acid molecules to a vertebrate subject using cationic microparticles. The microparticles comprise a polymer, such as a poly(α-hydroxy acid), a polyhydroxy butyric acid, a polycaprolactone, a polyorthoester, a polyanhydride, and the like, and are formed using cationic surfactants. Nucleic acid molecules are adsorbed on the surfaces of the microparticles.
Kim et al. (Pharmaceutical Research, vol. 18, pages 54-60, 2001) and Chung et al. (Journal of Controlled Release, volume 71, pages 339-350, 2001) describe various oil-in-water emulsion formulations that are used to enhance in vitro and in vivo transfection efficiency of DNA molecules.
Ott et al. (Journal of Controlled Release, volume 79, pages 1-5, 2002) describes an approach involving a cationic sub-micron emulsion as a delivery system/adjuvant for DNA. The sub-micron emulsion approach is based on MF59, a potent squalene in water adjuvant which has been manufactured at large scale and has been used in a commercially approved product (Fluad®). 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) was used to facilitate intracellular delivery of plasmid DNA.
Although DNA-based vaccines hold great promise for prevention and treatment of diseases, general concerns have been raised regarding their safety. The introduced DNA molecules could potentially integrate into the host genome or, due to their distribution to various tissues, could lead to undesirable sustained expression of antigens. In addition, certain DNA viruses have also been used as a vehicle to deliver DNA molecules. Because of their infectious properties, such viruses achieve a very high transfection rate. The viruses used are genetically modified in such a manner that no functional infectious particles are formed in the transfected cell. Despite these precautions, however, it is not possible to rule out the risk of uncontrolled propagation of the introduced gene and viral genes, for example due to potential recombination events. This also entails the risk of the DNA being inserted into an intact gene of the host cell's genome by e.g. recombination, with the consequence that this gene may be mutated and thus completely or partially inactivated or may give rise to misinformation. In other words, synthesis of a gene product which is vital to the cell may be completely suppressed or, alternatively, a modified or incorrect gene product is expressed. In addition, it is generally difficult to scale up the manufacture and purification of clinical-grade viral vectors.
One particular risk occurs if the DNA is integrated into a gene which is involved in the regulation of cell growth. In this case, the host cell may become degenerate and lead to cancer or tumor formation. Furthermore, if the DNA introduced into the cell is to be expressed, it is necessary for the corresponding DNA vehicle to contain a strong promoter, such as the viral CMV promoter. The integration of such promoters into the genome of the treated cell may result in unwanted alterations of the regulation of gene expression in the cell. Another risk of using DNA as an agent to induce an immune response (e.g. as a vaccine) is the induction of pathogenic anti-DNA antibodies in the patient into whom the foreign DNA has been introduced, so bringing about an undesirable immune response.
RNA molecules encoding an antigen or a derivative thereof may also be used as vaccines. RNA vaccines offer certain advantages as compared to DNA vaccines. First, RNA cannot integrate into the host genome thus abolishing the risk of malignancies. Second, due to the rapid degradation of RNA, expression of the foreign transgene is often short-lived, avoiding uncontrolled long term expression of the antigen. Third, RNA molecules only need to be delivered to the cytoplasm to express the encoded antigen, whereas DNA molecules must permeate through the nuclear membrane.
Nonetheless, compared with DNA-based vaccines, relatively minor attention has been given to RNA-based vaccines. RNAs and oligonucleotides are hydrophilic, negatively charged molecules that are highly susceptible to degradation by nucleases when administered as a therapeutic or vaccine. Additionally, RNAs and oligonucleotides are not actively transported into cells. See, e.g., Vajdy, M., et al., Mucosal adjuvants and delivery systemsfor protein-, DNA-and RNA-based vaccines, Immunol Cell Biol, 2004. 82(6): p. 617-27.
Ying et al. (Nature Medicine, vol. 5, pages 823-827, 1999) describes a self-replicating RNA vaccine in which naked RNA encoding β-galactosidase was delivered and the induction of CD8+ cells was reported.
Montana et al. (Bioconjugate Chem. 2007, 18, pages 302-308) describes using cationic solid-lipid nanoparticles as RNA carriers for gene transfer. It was shown that solid-lipid nanoparticles protected the RNA molecule from degradation, and the expression of reporter protein (fluorescein) was detected after microinjecting the RNA-particle complex into sea urchin eggs.
WO 2010/009277 discloses Nano Lipid Peptide Particles (NLPPs) comprising (a) an amphipathic peptide, (b) a lipid, and (c) at least one immunogenic species. In certain embodiments, the NLPPs also incorporate a positively charged “capturing agent,” such as a cationic lipid. The capturing agent is used to anchor a negatively charged immunogenic species (e.g., a DNA molecule or an RNA molecule). Preparation of NLPP requires amphipathic peptides, which are used to solubilize the lipid component and to form nano-particles.
Therefore, there is a need to provide delivery systems for nucleic acid molecules. The delivery systems are useful for nucleic acid-based vaccines, in particular RNA-based vaccines.